Warning!! CHKDSK Reduces Your Disk Space. But It’s For Your Good

🕔 3 minutes read

Regular computer users might encounter "CHKDSK" when troubleshooting system issues. Ever wondered how running CHKDSK impacts disk space? This article explores CHKDSK's effects on storage, helping you optimize computer performance and capacity.

Microsoft’s hard disk scanning and repair utility, CHKDSK (“check disk”), may not be unfamiliar to a common Windows user. It’s been in Windows for more than 2 decades. Even on Microsoft’s latest OS - Windows 10, this utility is available in both command line format and graphical format.

Running CHKDSK in Windows 10 is very simple. Just assure that you have administrative privileges for that. Sometimes, the check disk process may take a long time – particularly when you have a larger hard disk drive.

But today, let's not discuss “how to” questions. Instead, I’m thinking of addressing an issue – encountered by several users after running CHKDSK. Most of them have reported:

After running CHKDSK command, my hard disk space was found to be reduced to a considerable extent.

User Query

Probably, the first logical answer that comes to your mind when you read this issue is - it happened due to a bad command. But that's not entirely true.

Reasons Behind the Reduction

The reduction in disk space after running CHKDSK can be attributed to a few key reasons:

  • Bad Sector Marking: When CHKDSK encounters a bad sector, it marks it as unusable to prevent data from being written to that area. This proactive approach safeguards your data but effectively reduces the usable space on your drive.
  • Data Relocation: If CHKDSK detects data in sectors that are starting to show signs of deterioration, it may relocate that data to healthier sectors. While this prevents potential data loss, it can result in fragmented storage and reduced available space.
  • System Files Overhead: CHKDSK itself requires some space to operate. When it runs, it might create log files and temporary data that occupy additional space on your drive

Allow me to dig deep into the topic

Basically, CHKDSK is a file system integrity verifier. It fixes logical file system errors and marks bad sectors on the disk surface. The whole CHKDSK activity can be divided into 5 phases, where 4th and 5th phases are optional.

1st phase (Check for Consistency):

Here, CHKDSK examines each and every file record segment of a volume to its Master File Table (MFT) for internal consistency.

2nd Phase (Checking Indexes)

In this phase, CHKDSK checks each directory on the volume and verifies that every file or subdirectory referenced in a directory exists as a valid file record in the MFT. It also checks for circular directory references.

3rd Phase (Checking Security Descriptors)

Here, CHKDSK verifies the security descriptor associated with files/directories. These descriptors contain information about the ownership of a file/directory, file permissions, etc.

4th & 5th Phases (Checking Sectors – Optional)

If a user wants, he/she can go with this additional step. Here in the 4th phase, CHKDSK verifies the clusters in use. In the 5th phase, CHKDSK verifies clusters currently not in use. These phases may consume more time depending on the size of the drive.

Now, you’ve got some idea on the topic. So, it’s easy for me to explain the real cause of the problem.

Checking sectors using CHKDSK is an optional phase in the process. People who have noticed a reduction in their disk spaces after CHKDSK might have chosen this option to check bad sectors on the drive. What eventually happened would be – more bad sectors are marked and blocked by CHKDSK. As the number of bad sectors increases, a user can see a significant reduction in his/her hard disk space.

The increase in the number of these bad sectors could be a serious problem as it indicates the possible failure of a hard drive. With CHKDSK, you can either skip scanning for bad sectors or try to recover data from those sectors. But there’s an undeniable fact – some data may be corrupted.

Interesting Read: Find out how to recover files deleted by chkdsk.

Managing Disk Space Effectively

While the reduction in disk space might seem concerning, there are several steps you can take to manage your storage effectively:

  1. Regular Backups: Keeping regular backups of your important data ensures that even if CHKDSK makes changes to your drive, you won't lose any critical files.
  2. Frequent Maintenance: Perform regular disk cleanup and defragmentation to minimize the impact of data relocation and fragmentation caused by CHKDSK.
  3. Monitor Disk Usage: Keep an eye on your disk usage over time. If you notice a significant decrease in available space after running CHKDSK, it might be an indication of deeper issues that need attention.


Sectors of a hard drive may become bad/defective due to a number of reasons – especially aging. CHKDSK is a utility that alerts you to the need to take care of your valuable files by mapping bad sectors on a drive. Also, this utility attempts to recover data from those defective sectors up to an extent. So, trusting this utility won’t cause any harm; actually, it's a good sign that you got to know about your hard drive's health.

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John Harris

With a decade of experience in data recovery, John Harris, Senior Editor at Remo Software, is your go-to specialist. His focus includes partition management, Windows solutions, and data troubleshooting, delivering insightful content that serves both users and search engines.

John's expertise shines through in illuminating blog posts, untangling data loss intricacies across diverse storage platforms. His mastery extends from file systems to SD cards, USBs, and external drives on Mac and Windows.

Recognized by cpomagazine, everythingusb, and more, John Harris is your trusted data recovery guide. You can also find his articles featured on correctblogger.com, computertechreviews.

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